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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

25

their salts, iron, mineral salts, saccharine substances, albuminoids, gummy
matters, etc., and sometimes alcohol (up to 1-5% by volume). Concentrated
lemon juice contains about 40% of citric acid and has the density 1-2-1-4. The
crude juice has the density 1-03-1-04 and contains variable proportions of citric
acid (4-7%). The crude and concentrated juices from the bergamot contain
less citric acid than lemon juice (about 30% in the concentrated juice).

These juices may be adulterated with salt, which increases the density, or
with sulphuric, tartaric or nitric acid, which increases the acidity. The pure
juices should contain only traces of sulphates and chlorides.

These juices are usually quoted in English measures, the unit of volume being
taken as the pipe of 108 imperial gallons (i gallon = 4-536 litres) and that of
weight as the ounce (28-35 grams). The crude juice is quoted on the basis of
ii ozs. of citric acid per gallon, and the concentrated juice on the basis of 66-87
ozs. of free crystallised citric acid (C8H8O7, H2O) or 64 ozs. of the acid, C8H8O7,
£ H2O. Bergamot juice is generally quoted on the basis of 48 ozs. per gallon.

FORMIC   ACID

HaCOa = 46

In the pure state this is a colourless liquid of particularly pungent odour,
D = 1-225-1-227 (at 15°), b.pt. 100°; it is extremely soluble in water
and at o° solidifies to crystals which melt again at about 8°. It is placed
on the market in various concentrations, up to almost 100%, but usually
85% (D = 1-202).

It may contain mineral acids (especially hydrochloric acid), acetic acid
(mixtures of formic acid with varying proportions of acetic acid are sold
as acetargol), oxalic acid, salts of the alkalies and heavy metals (lead, copper,
iron), arsenic (occasional traces), acrolein, allyl alcohol and empyreumatic
substances. The following tests are made.

1.   Mineral Acids.—10 c.c. of the acid are diluted with 100 c.c. of
water, 50 c.c. being then treated with silver nitrate (in the cold) and 50 c.c.
with barium chloride.

2.  Acetic Acid.—1-2 c.c. of the acid, diluted with 20 c.c. of water
and mixed with 6,'grams of yellow mercuric oxide, are heated on the water-
bath until evolution of gas (C02) ceases and the liquid then filtered.    In
the case of pure formic acid, the filtrate has a neutral reaction (all the forrjf^1
acid being decomposed), but in presence of acetic acid the filtrate is afpk#(h
and permits of the identification of the acetic acid by the odour.           '*>*£

The quantitative determination of acetic acid when mixed with for$a|^'
acid may be effected by Hamel's method : 3-4 grams of the acid are, nj*tf»
tralised with N-sodium hydroxide (towards phenolphthalein), the liq$LieT
evaporated to dryness on a water-bath and the residue dried in an oveit' 'ai
120-130° and weighed. It is then treated with excess of pure formic
(which liberates acetic acid from its salts), again evaporated to
the residue being then taken up in a little water, once more evapoi%te$
and the residue dried at 120-130° and weighed. From the difference
between the two weights the acetic acid is calculated.                        -jl ,

3.   Oxalic Acid.—2 c.c. of the acid are diluted with 20 c.c. of Abater
and the liquid rendered alkaline with ammonia and treated with ca^iiim
chloride;   a turbidity indicates oxalic acid.                                            ^'--;'

4.  Various Mineral Salts.—10 c.c. of the acid, evaporated on aly for delicate colours, should not contain iron.                                                                       l.2o